Destroyer Bio #102

[MTD52]

---

Members do not see this ad.

Anyone know how to figure out that pedigree problem?

 

[nze82]

Anyone know how to figure out that pedigree problem?

What's the problem asking?

 

[MTD52]

Consider the following pedigree (I don't have a picture):

What is the most likely mode of inheritance?
a) X-linked recessive
b) X-linked dominant
c) autosomal dominant
d) autosomal recessive
e) none of these without more information

 

[nze82]

Consider the following pedigree (I don't have a picture):

What is the most likely mode of inheritance?
a) X-linked recessive
b) X-linked dominant
c) autosomal dominant
d) autosomal recessive
e) none of these without more information

Well, I don't have the book. So, I can't provide you with an exact answer. But I can give you a general guideline on how to approach such problems.

1-Look at the generations. Does the trait of interest skip few generations and reappear again? If yes, you're looking at a recessive trait. Another way you can detect a recessive trait is to look for unaffected parents who have at least one affected child.
If no (If the trait appears in each and every generation), then you're looking at a dominant trait. Another way you can detect a dominant trait is that at least one parent of any affected child, must be affected.

This alone should help you eliminate some of the wrong choices and narrow down your answer.
Now that we know how to determine whether the trait is recessive or not, let's move on and determine whether its Autosomal or X-linked:

1-X-linked traits are gender specific and they are more common in males as oppose to females. So, look in your pedigree. If the trait only shows up in a specific gender, then you're most likely looking at an X-linked trait.
If the trait appears in both males and females, then it's most likely Autosomal.

Hope this info will help you find the correct answer.

 

[UCB05]

Consider the following pedigree (I don't have a picture):

What is the most likely mode of inheritance?
a) X-linked recessive
b) X-linked dominant
c) autosomal dominant
d) autosomal recessive
e) none of these without more information

I have the 2008 version, so i hope the table hasn't changed 😛

The mating of the first-generation afflicted female and normal male produces among others, a normal and abnormal males. That implies, if the gene were X-linked recessive, that the mother is heterozygous. They also have a normal daughter and an afflicted daughter. Since the father was normal, you can rule out X-linked recessive, as his X was normal and the afflicted daughters would have to be heterozygous.

In the second generation mating of afflicted male and normal female, they have an afflicted son, which rules out X-linked dominant. If it were X-linked dominant, since the mother was normal, it would not have been possible for the son inherit a mutant X from either parent.

So it has to be autosomal. Each set of offspring from a pairing produces afflicted offspring. If the gene were recessive, that would have to imply the cosmic improbability (barring incest and VERY common gene frequency) that the unafflicted great-grandfather, unrelated grandmother, and unrelated mother on the left were all carriers for the gene, for it to show up in every generation of offspring. The more likely case is that it's autosomal dominant.

 

[MTD52]

Great advice thus far. Thank you 🙂. I'll check out the problem again later and get back to you.